A linear motor according to the present invention is not only an electric motor whose runner moves relative to the stator on a straight path, but also an electric motor whose runner moves relative to the stator on a curved path, for example on a circular path, namely whose runner rotates about an axis, wherein the coils of the stator are arranged opposite to the permanent magnets of the runner in axial direction and not in radial direction like in a classic electric motor.
For many industrial applications it is required to perform short stroke linear movements with high acceleration and high precision. This is the case for example for so called pick and place machines when manufacturing semi conductor circuits. It is known to use linear motors for short stroke movements. High accelerations in combination with large force development are achieved in linear motors when a magnetic field of the permanent magnets is run through a back iron. Thus, in known linear motors the permanent magnets are arranged on a back iron device and the electrical coils are arranged in the runner or at the runner so that the coils with the runner move relative to the magnet arrangement arranged on the back device. In a device of this type on the one hand side the mass of the coils has to be moved along and certainly also accelerated along and furthermore it is required to transmit the electrical supply for the coils to the moveable runner of the linear motor which is performed through flexible electrical conduits for short stroke movements.
However, when particularly high accelerations have to be performed in combinations with short paths, thus with frequent acceleration direction reversals as it is the case for pick and place machines, it is often detrimental to move the mass of the coils along.
Furthermore linear motors of this type are often configured so that the runners form a yoke that laterally reaches over the magnet assembly laterally and in which the yoke pillars are supported on the back iron device or adjacent thereto. This causes a width of the linear motor which is significantly wider than a width of a permanent magnet arrangement. Since the pull force between coils and permanent magnet arrangement is arranged in a center of the yoke, the runner also has to be configured very stable in order to support bending loads caused by the bending moments caused by the magnetic force.
US 2007/011485 A1 illustrates and describes a linear actuator with moving permanent magnets. This linear actuator includes a stator on which the armature windings are arranged, a moveable slide including the permanent magnets and a back iron yoke arranged in a stationary manner on the side of the slide that is oriented away from the stator. The moveable slide has a cross section shaped as an inverted U and is supported at its lateral free ends through conventional bearings on a support rail. This lateral bearing support causes bending moments in the center section of the U which connects both arms, wherein the bending moments have to be supported through a respective material thickness.
US 2009 01 67 103 A1 illustrates and describes a permanent magnet arrangement on a rotor. The permanent magnets are arranged at on outer circumference of the rotor on a rotor element, wherein a small distance is provided in circumferential direction between the individual permanent magnets.
DE 101 42 642 A1 illustrates and describes an electric motor, in particular a linear motor in which the windings of the armature are air cooled.
DE 199 06 4 A1 illustrates and describes a secondary element for a linear motor in which permanent magnets are placed on a metal carrier plate and secured against movement thereon, wherein the entire arrangement is encased in an encasement compound. The encased element thus formed encases the permanent magnets.
US 2004/0239194 illustrates and describes a permanent magnet arrangement for a linear motor in which the permanent magnets are arranged with alternating polarity on a carrier configured as a magnetically conductive plate acting as a back iron. The plate is moveable in a linear manner along an armature that is provided with electromagnetic coils.
U.S. Pat. No. 4,798,895 A discloses a linear motor with an air supported runner, wherein the runner includes the back iron. The runner which is either configured flat or as an inverted U is supported with its free ends at the stator, wherein bending moments impact the runner in its center portion, namely where the magnetic forces are effective.
US 2006/0139615 A1 illustrates and describes a lithography device with a moveable slide which is air supported on a stator and moveable in a linear manner. The slide forming the runner is supported at the stator through air bearings, wherein the compressed air providing the bearing pressure is run through conduits in the slide to nozzles provided in the slide. The permanent magnets are integrated in the body of the slide above the conduit system for the support air. A back iron device is arranged in a stationary manner on a side of the slide that is oriented away from the stator and connected with a coil element, so that the back iron device is arranged on a side of the coils that is oriented away from the permanent magnets of the slide.